Along with increase of train speed, traffic volume and axle loading, the rate of wear-out failure for a rail increases dramatically due to a dual effect of impact and wear caused by wheels. Conventional methods for improving life of rails throughout the world mainly focus on two aspects, namely heat treatment methods for rail and rail materials. With rapid development of laser technologies, methods of laser surface strengthening have been applied to rail for surface treating by domestic and foreign scholars, and good experimental results have been achieved.
The conventional method can only be accomplished in workshops; however, besides the laser surface strengthening method can facilitate fixed-point processing in workshops, the specific mobile equipment can be developed in order to take laser processing equipments into the railway field for on-line laser treating on rail.
A Chinese utility model ‘Laser maintenance vehicle for rail’ (Pub. No.: CN2622241Y, Pub. Date: Jun. 30, 2004) provides a laser maintenance vehicle for rail, the laser maintenance vehicle for rail includes two parts: a traction-control vehicle and a rail-operation vehicle. The traction-control vehicle is modified on the basis of a railway motor-trolley, the main difference therebetween is that a laser-operation console is disposed at the driver position of the railway motor-trolley; the rail-operation vehicle is modified on the basis of a railway passenger car which is equipped with one or two high-power CO2 laser. A laser optical path and a numerical control system are set up to accurately transmit laser beam to the processing point on rail. To assure laser work on rail can be successfully accomplished, the laser maintenance vehicle for rail also includes a vehicle damping system, a laser damping system, a rust cleaning system for a rail surface, a spraying system for light-absorbing coatings on rail surface, a drying system for coatings, a gas supply system for laser, a powder supply system for laser, a cooling system for laser, a laser vehicle body, a monitoring and illuminating system, a body sealing and dust removing system, etc, other than a lasers system, a laser optical path and a mobile numerical control system.
According to the above description, the laser maintenance vehicle has several shortcomings as follows:
Firstly, the device uses the high-power CO2 laser as a light source; the photoelectric conversion efficiency thereof is relatively low, while energy consumption thereof is high. The wavelength of the CO2 laser is 10.6 microns, therefrom the absorption of a metal substrate to that is quiet low, and the procedure is comparatively complicated because the laser processing cannot be carried out until light-absorbing coatings are sprayed thereon and dried. Since a light-guide system of the CO2 laser can only use a flying light path or a hard-light-path system for transmission, precision of the light-guide system may be inevitably affected by vibration generated by the laser maintenance vehicle during operation, and it is difficult to ensure long-term stability of laser processing.
Secondly, when the device carries out laser maintenance, the laser maintenance vehicle is stationary, and the maximum distance for a laser processing head moving along the rail is 1000 mm. The distance of a rail processed by the laser processing head at one time is limited by the length of the body of the laser maintenance vehicle due to the coming to a standstill of the laser maintenance vehicle, and thus making it inconvenient for long-distance repairing. Further, when the laser vehicle is to arrive to the next section of a rail to be repaired, since a movement distance of the traction-control vehicle cannot be accurate to centimeters, it is difficult for the traction-control vehicle to be precisely located.
Thirdly, compared with the concerned accurate trajectories required for laser processing, the overall accuracy of a railway line in a railway field is good, but an actual rail is a curve line erratically fluctuated along an overall route. A position of the laser processing head can not be adjusted in real time in the invention, thus it is difficult to ensure for the laser processing head to guarantee an accuracy of hardening a processing path.
In view of the drawbacks with the above-mentioned patent literature, in 2008, Chinese invention discloses an ‘On-line laser processing device for strengthening treatment of rail surface’ (Patent No.: 200810169671.5). The on-line laser processing device divides a laser processing system into two parts: a laser processing trolley and a power engineering vehicle. The laser processing trolley is small volume, light weight, good flexibility, and convenient loading and unloading, and is capable of effectively dodging trains, and facilitating various on-line strengthening treatment on rail; the power engineering vehicle includes devices with relatively large weight, such as a generator, a chiller, an air compressor, a cold dryer, a high-voltage power supply for a laser, a control system, and so on. By using a solid state laser as a light source capable of transmitting by fiber, the invention saves a complicated flying light path, and reduces loss of laser energy transmitted in an optical path; a laser used thereby emits a near-infrared laser with a wavelength of 1064 nmn, and absorption of the rail to the laser is high, therefore, procedures of pre-spraying coating and cleaning coating following thereby are not required, and thus simplifying the process, and reducing volume, weight, power consumption and cost of the device.
However, the above-mentioned on-line laser processing device still has the following shortcomings:
Firstly, the small laser processing trolley and the power engineering vehicle are two separated parts, the maximum distance of an interconnected fiber or a cable is 100 meters, which increases complexity of the device used in railway field; compared with a complete set of integrated equipment system, its reliability thereof is relatively low.
Secondly, although the small laser processing trolley is small volume, light weight and good flexibility, manpower or a small forklift is required to install it on a track, and connection and device adjustment of the fiber or the cable system need to be conducted on the track, therefore, effective time and processing efficiency of laser strengthening-toughening treatment on railway track are affected.
Thirdly, the way of approaching the railway track by the power engineering vehicle of the on-line laser processing device is sometimes limited. In some special places (such as mountain railways), the power engineering vehicle cannot conveniently approach railway tracks, and wheel systems thereof cannot directly travel thereon, which result in limitation of the combined type small laser processing trolley and power engineering vehicle on line laser processing device in terms of application range and efficiency.
In summary, how to further improve mobility of an on-line laser processing device and accuracy of a laser processing track for rail is a key to ensure application of the technology in railway transit. As for the on-line laser processing device, if it can both maintain accurate motion on a railway and quickly leave therefrom after laser processing, obviously more practical value is possible. In addition, the device should also possess basic features of an independent laser processing system, namely comprising a laser, a light guide system, a chiller, an air compressor, a cold dryer, a powder feeder, a movement actuators, a laser processing head, a control system, and so on, so that it can be applied to on-line laser strengthening-toughening treatment and laser cladding repairing for rail.